Means for prevention of static electric discharge on motion picture projector reels

ABSTRACT

This disclosure relates to a structure used to prevent the buildup of high voltage static electric charge on the flanges or support hub of motion picture reels. A conductive coating is placed around the nonconductive areas of the connection between the flanges and ground potential so that the accumulation of discharge potentials is prevented.

United States Patent Edward S. McKee Rochester, N.Y.

Feb. 19, 1969 June 15, I971 Eastman Kodak Company Rochester, N.Y.

Inventor App]. No. Filed Patented Assignee MEANS FOR PREVENTION OF STATIC ELECTRIC DISCHARGE ON MOTION-PICTURE PROJECTOR REELS 2 Claims, 1 Drawing Fig.

us. c|..' 317/2, 242/55.l 1 Int. Cl H05! 3/00, HOSf 3/02 Field of Search 242/71.8;

[56] References Cited UNITED STATES PATENTS 1,848,871 3/1932 Corlette et a1. 317/2 2,339,009 1/1944 Gordon 242/71.8 2,854,199 9/1958 Boyer 242/7l.8 2,992,789 7/1961 Sardeson 242/7 1 .8

Primary Examiner-Lee T. I-Iix Assistant Examiner-C. L. Yates Attorneys- Robert W. Hampton and James J. Wood ABSTRACT: This disclosure relates to a structure used to prevent the buildup of high voltage static electric charge on the flanges or support hub of motion picture reels. A conductive coating is placed around the nonconductive areas of the connection between the flanges and ground potential so that the accumulation of discharge potentials is prevented.

PATENIEU JUNI 51971 E E K c M S D m W D E INVENTOR.

ATTORNEYS MEANS FOR PREVENTION OF STATIC ELECTRIC DISCHARGE ON MOTION-PICTURE PROJECTOR REELS BACKGROUND OF THE INVENTION l. Field of the Invention This invention relates to means for the prevention of static electric buildup on motion picture projector reels.

2. Description of the Prior Art The annoying and sometimes harmful effects produced by electrostatic discharges have been a problem in many industries.

The term static electricity or triboelectricity usually implies manifestations of electric charge accumulations resulting in interesting, useful, or undesirable phenomena.

The invention here, however, is concerned with those charge accumulations which often produce annoying and even dangerous efi'ects. Those considerations are important particularly in the motion-picture projector field where static electric charge accumulations my produce electrostatic attractions of dust, lint, and light particles to surfaces such as phonographic records, photographic films, and high precision apparatus which may frequently impair performance. In particular in motion-picture practice, the large concentrations of charge can produce annoying and even dangerous effects to the operator, and in addition, even in those-situations where the effects and simply annoying, nevertheless, the discharge produces electromagnetic radiation which propagates over considerable distances and may find its way into the audio amplifying equipment to produce deleterious results in the quality of reception by reason of the familiar noise disturbances.

Static electricity effects depend on the excess of charge of one sign existing on a macroscopic basis in one or more locations with respect to charge groups of opposite sign. Static electricity effects as generally understood frequently result from mechanical rubbing or impact processes. When two dissimilar substances are rubbed together they become electrified with opposite polarities. The frictional action probably serves to accentuate the contact potential differences normally existing between different substances. Many modern plastics, such as polystyrene, while excellent insulators nevertheless, are easily electrified by frictional effects produced even by ordinary handling.

The prior art has struggled to eliminate or at least alleviate these problems. For example, U.S. Pat. No. 1,206,357 to Nusbaum teaches the prevention of the generation of static electricity in motion-picture apparatus by insuring that, a predetermined portion of the material of the apparatus, the parts of which are in moving contact with the film, is of the same electrostatic characteristics as the film itself in order to prevent the buildup of charge. Nusbaum is primarily interested in preventing electrostatic discharge because the resulting sparks could ruin the film.

U.S. Pat. No. l,848,87l to'E. H. Corlett etal. eliminates static electricity in a film camera by placing conductive material, such as tinfoil, on the back of the entire area of film, rolling metallic sheet and the film on a spool so that they will being alternate 'convolutions, and grounding the metallic sheet to the metallic body of the camera.

U.S. Pat. No. l,530,704 to Thomson teaches the prevention of electrostatic charge buildup by the use of a flat graphite conducting member, such as a cloth membrane or plate which is covered with graphite, and which is in close contact with the unexposed side of the film, so that the film in its travel between guide rollers successively discharges the buildup of static electricity.

SUMMARY OF THE INVENTION An object of the present invention is to provide an electrically conductive path between the metallic flanges of a film reel and a point of ground potential on apparatus for receiving such reels when the flanges are supported by a member having electrical insulator properties.

In accordance with the above object, the illustrated embodiment of the present invention includes a motion picture projector adapted to receive a takeup or supply film reel comprising two metal flanges and a plastic core. The projector is provided with a plastic spindle which is attached to a metal spindle shaft. The shaft is electrically grounded and a conductive coating on the plastic spindle provides a conductive path between the reel flanges and the shaft.

The novel features of the invention are set forth with particularity in the appended claims, the invention itself however, both as to its organization and method of operation together with further objects and advantages thereof may best be understood by reference to the description to follow considered in connection with the accompanying drawing.

BRIEF DESCRIPTION OF THE DRAWING FIG. 1 is a sectional view of a motion-picture reel means utilizing means for the prevention of high voltage static electric buildup on motion-picture reels in accordance with the invention.

Referring now to FIG. 1 the motion-picture projector reel in accordance with one embodiment is indicated generally at 10. The reel comprises metallic flanges 12 and 14 positioned in spaced relationship by means of a plastic ring core 16.

The reel 10 in the illustrated embodiment is adopted for mounting on a projector indicated generally in part sectional view at 24. The projector 24 comprises a frame 26, supporting a metallic bearing 28, which in turn supports a metallic spindle shaft 30. The shaft 30 includes a splined portion, indicated at 32, over which a plastic spindle 18 is nonrotatably forced in order to secure the spindle on shaft 30. Photographic film is indicated at 34. A conductive coating 22 is deposited around the outer geometrical outline of spindle 18 to provide a conductive path between flanges l2 and 14 of reel 10 and shaft 30.

In the practice of the invention the motion-picture projector reel builds up a charge of static electricity on metallic flanges l2 and 14 both from the handling of the reel itself by the operator and by the motion of the photographic film. The macroscopic charges built up are considerable, and may' reach several thousand volts. It is not at all unusual to observe a spark jump through a distance of one-eighth inch or so. Knowing the dielectric strength of air it can readily be calculated that this discharge potential is in the order of several thousand volts. Additionally, the trapped charge buildup depends in great measure upon atmospheric conditions. For example a high atmospheric humidity, helps to increase the circuit linkage conductivity, so that not as great a charge will buildup. The converse is true when atmospheric humidity is low. With the provision of the conductive coating 22 on the spindle, the accumulated charges are bled off. As indicated by the arrow 36 the trapped charge on the flange l2 migrates toward the conductive coating 22 where it is conveyed as indicated by the successive arrows: 38, 40, 42, 44 to the metallic shaft 30. The frame of the device may be preferably grounded as indicated, but even if ungrounded, the electrical sink presented by the large metallic area of the frame will assist in the dissipation of the charge. Similarly the charge on flange 14 is leaked off in a path as indicated by the arrows identified successively at: 46, 42, 44 to the same metallic shaft 30.

The invention has been described in detail with particular reference to a preferred embodiment thereof, but it will be understood that variations and modifications can be effected within the spirit and scope of the invention.

I claim:

1. Apparatus for preventing the buildup of static charges on film reels of the type. having metal flanges, said apparatus comprising:

a source-of ground potential;

a rotatable shaft;

electrical insulator support means for mounting the reels on said shaft; and

ground; said support means comprises a plastic spindle fixed to said shaft for rotation therewith; and said conductive coating is positioned to provide a low resistance path between the flanges of a received reel and said shaft. 

1. Apparatus for preventing the buildup of static charges on film reels of the type having metal flanges, said apparatus comprising: a source of ground potential; a rotatable shaft; electrical insulator support means for mounting the reels on said shaft; and an electrically conductive coating on said support means, said conductive coating being positioned to make good electrical contact with the flanges of a mounted reel and with said source of ground potential to provide a low resistance path between the reel flanges and ground.
 2. Apparatus as defined in claim 1 wherein: said shaft is electrically conductive and is connected to ground; said support means comprises a plastic spindle fixed to said shaft for rotation therewith; and said conductive coating is positioned to provide a low resistance path between the flanges of a received reel and said shaft. 